How Do I Add a Standalone ESXi Host to vCenter Server

You can use the vSphere AutomationREST APIs to add a standalone host to a vCenter Server instance.

Add a single ESXi host to a vCenter Server instance by using the POST https://<vcenter_ip_address_or_fqdn>/api/vcenter/host request and submitting a HostCreateSpec JSON object in the request body. When you construct the host object, make sure that you set values for the IP address or the DNS resolvable host name and the administrator credentials.